Heat sink device

ABSTRACT

A heat radiator  1  includes an insulating substrate  3  whose first side serves as a heat-generating-element-mounting side, and a heat sink  5  fixed to a second side of the insulating substrate  3.  A metal layer  7  is formed on a side of the insulating substrate  3  opposite the heat-generating-element-mounting side. A stress relaxation member  4  intervenes between the metal layer  7  of the insulating substrate  3  and the heat sink  5.  The stress relaxation member  4  is formed of an aluminum plate  10  having a plurality of through holes  9  formed therein, and the through holes  9  serve as stress-absorbing spaces. The stress relaxation member  4  is brazed to the metal layer  7  of the insulating substrate  3  and to the heat sink  5.  This heat radiator  1  is low in material cost and exhibits excellent heat radiation performance.

TECHNICAL FIELD

The present invention relates to a heat radiator, and more particularlyto a heat radiator which includes an insulating substrate whose firstside serves as a heat-generating-element-mounting side, and a heat sinkfixed to a second side of the insulating substrate and which radiates,from the heat sink, heat generated from a heat-generating-element, suchas a semiconductor device, mounted on the insulating substrate.

The term “aluminum” as used herein and in the appended claimsencompasses aluminum alloys in addition to pure aluminum, except for thecase where “pure aluminum” is specified.

BACKGROUND ART

In a power module which uses a semiconductor device, such as an IGBT(Insulated Gate Bipolar Transistor), the semiconductor device must beheld at a predetermined temperature or lower by means of efficientlyradiating heat generated therefrom. Conventionally, in order to meet therequirement, a heat radiator is used. The heat radiator includes aninsulating substrate which is formed of a ceramic, such as Al₂O₃ or AlN,and whose first side serves as a heat-generating-element-mounting side,and a heat sink which is formed of a high-thermal-conduction metal, suchas aluminum or copper (including copper alloys; hereinafter, the same isapplied), and is soldered to a second side of the insulating substrate.A semiconductor device is soldered to theheat-generating-element-mounting side of the insulating substrate of theheat radiator, thereby forming the power module.

A power module used in, for example, a hybrid car must maintain the heatradiation performance of a heat radiator over a long term. Theabove-mentioned conventional heat radiator involves the followingproblem. Under some working conditions, thermal stress arises from adifference in thermal expansion coefficient between the insulatingsubstrate and the heat sink and causes cracking in the insulatingsubstrate, cracking in a solder layer which bonds the insulatingsubstrate and the heat sink together, or warpage of a bond surface ofthe heat sink bonded to the insulating substrate. Such cracking orwarpage impairs heat radiation performance.

A proposed heat radiator in which the above problem is solved includesan insulating substrate whose first side serves as aheat-generating-element-mounting side, a heat radiation member which issoldered to a second side of the insulating substrate, and a heat sinkwhich is screwed on the heat radiation member. The heat radiation memberincludes a pair of platelike heat-radiation-member bodies formed of ahigh-thermal-conduction material, such as aluminum or copper, and alow-thermal-expansion material, such as an Invar alloy, interveningbetween the platelike heat-radiation-member bodies. (Refer to PatentDocument 1)

However, the heat radiator described in Patent Document 1 must use theheat radiation member formed of a high-thermal-conduction material and alow-thermal-expansion material; thus, material cost is increased.Furthermore, since the heat radiation member and the heat sink aremerely screwed together, thermal conduction therebetween isinsufficient, resulting in a failure to provide sufficient heatradiation performance.

Patent Document 1: Japanese Patent Application Laid-Open (kokai) No.2004-153075

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to solve the above problem and toprovide a heat radiator whose material cost is low and which exhibitsexcellent heat radiation performance.

Means for solving the Problems

To achieve the above object, the present invention comprises thefollowing modes.

1) A heat radiator comprising an insulating substrate whose first sideserves as a heat-generating-element-mounting side, and a heat sink fixedto a second side of the insulating substrate;

wherein a stress relaxation member formed of a high-thermal-conductionmaterial and having a stress-absorbing space intervenes between thesecond side of the insulating substrate and the heat sink, and thestress relaxation member is metal-bonded to the insulating substrate andto the heat sink.

2) A heat radiator according to par. 1), wherein the stress relaxationmember is brazed to the insulating substrate and to the heat sink.

3) A heat radiator comprising an insulating substrate whose first sideserves as a heat-generating-element-mounting side, and a heat sink fixedto a second side of the insulating substrate;

wherein a metal layer is formed on a side of the insulating substrateopposite the heat-generating-element-mounting side; a stress relaxationmember formed of a high-thermal-conduction material and having astress-absorbing space intervenes between the metal layer and the heatsink; and the stress relaxation member is metal-bonded to the metallayer of the insulating substrate and to the heat sink.

4) A heat radiator according to par. 3), wherein the stress relaxationmember is brazed to the metal layer of the insulating substrate and tothe heat sink.

5) A heat radiator according to any one of pars. 1) to 4), wherein theinsulating substrate is formed of a ceramic.

6) A heat radiator according to any one of pars. 1) to 5), wherein thestress relaxation member is formed of an aluminum plate having aplurality of through holes formed therein, and the through holes serveas the stress-absorbing spaces.

7) A heat radiator according to par. 6), wherein the through holes areformed in at least a portion of the aluminum plate which corresponds toa perimetric portion of the insulating substrate.

8) A heat radiator according to par. 6) or 7), wherein the through holesare of a non-angular shape and have a circle-equivalent diameter of 1 mmto 4 mm.

The term “non-angular” as used herein and in the appended claims refersto a shape which does not have a mathematically defined acute angle,obtuse angle, or right angle; for example, a circle, an ellipse, anelongated circle, or a substantially polygonal shape whose corners arerounded. The term “circle-equivalent diameter” as used herein and in theappended claims refers to the diameter of a circle whose area is equalto that of a shape in question.

In the heat radiator of par. 8), the through holes have acircle-equivalent diameter of 1 mm to 4 mm, for the following reason. Ifthe circle-equivalent diameter of the through holes is too small,deformation of the stress relaxation member may become insufficient whenthermal stress arises in the heat radiator from a difference in thermalexpansion coefficient between the insulating substrate and the heatsink, with the potential result that the stress relaxation member failsto exhibit sufficient stress-relaxing performance. If thecircle-equivalent diameter of the through holes is too large, thermalconductivity may drop. Particularly, in the case where the stressrelaxation member is brazed to the insulating substrate and to the heatsink, if the circle-equivalent diameter is too small, the through holesmay be filled with a brazing material, with the potential result thatthe stress relaxation member is not deformed at all even when thermalstress arises in the heat radiator.

9) A heat radiator according to any one of pars. 6) to 8), wherein apercentage of a total area of all of the through holes to an area of oneside of the aluminum plate is 3% to 50%.

In the heat radiator of par. 9), the percentage of the total area of allof the through holes to the area of one side of the aluminum plate is 3%to 50%, for the following reason. If the percentage is too low,deformation of the stress relaxation member may become insufficient whenthermal stress arises in the heat radiator from a difference in thermalexpansion coefficient between the insulating substrate and the heatsink, with the potential result that the stress relaxation member failsto exhibit sufficient stress-relaxing performance. If the percentage istoo high, thermal conductivity may drop.

10) A heat radiator according to any one of pars. 1) to 5), wherein thestress relaxation member is formed of an aluminum plate having aplurality of recesses formed on at least either side, and the recessesserve as the stress-absorbing spaces.

11) A heat radiator according to par. 10), wherein the recesses areformed on at least a portion of the aluminum plate which corresponds toa perimetric portion of the insulating substrate.

12) A heat radiator according to par. 10) or 11), wherein the openingsof the recesses are of a non-angular shape and have a circle-equivalentdiameter of 1 mm to 4 mm.

In the heat radiator of par. 12), the openings of the recesses have acircle-equivalent diameter of 1 mm to 4 mm, for the following reason. Ifthe circle-equivalent diameter of the openings of the recesses is toosmall, deformation of the stress relaxation member may becomeinsufficient when thermal stress arises in the heat radiator from adifference in thermal expansion coefficient between the insulatingsubstrate and the heat sink, with the potential result that the stressrelaxation member fails to exhibit sufficient stress-relaxingperformance. If the circle-equivalent diameter of the openings of therecesses is too large, thermal conductivity may drop. Particularly, inthe case where the stress relaxation member is brazed to the insulatingsubstrate and to the heat sink, if the circle-equivalent diameter is toosmall, the recesses may be filled with a brazing material, with thepotential result that the stress relaxation member is not deformed atall even when thermal stress arises in the heat radiator.

13) A heat radiator according to any one of pars. 10) to 12), wherein apercentage of a total area of openings of all of the recesses to an areaof a side of the aluminum plate on which the recesses are formed is 3%to 50%.

In the heat radiator of par. 13), the percentage of the total area ofopenings of all of the through holes to the area of the side of thealuminum plate on which the recesses are formed is 3% to 50%, for thefollowing reason. If the percentage is too low, deformation of thestress relaxation member may become insufficient when thermal stressarises in the heat radiator from a difference in thermal expansioncoefficient between the insulating substrate and the heat sink, with thepotential result that the stress relaxation member fails to exhibitsufficient stress-relaxing performance. If the percentage is too high,thermal conductivity may drop.

14) A heat radiator according to any one of pars. 1) to 5), wherein thestress relaxation member is formed of an aluminum plate having aplurality of recesses formed on at least either side and a plurality ofthrough holes formed therein, and the recesses and through holes serveas the stress-absorbing spaces.

15) A heat radiator according to any one of pars. 6) to 14), wherein thealuminum plate used to form the stress relaxation member has a thicknessof 0.3 mm to 3 mm.

In the heat radiator of par. 15), the aluminum plate used to form thestress relaxation member has a thickness of 0.3 mm to 3 mm, for thefollowing reason. If the aluminum plate is too thin, deformation of thestress relaxation member may become insufficient when thermal stressarises in the heat radiator from a difference in thermal expansioncoefficient between the insulating substrate and the heat sink, with thepotential result that the stress relaxation member fails to exhibitsufficient stress-relaxing performance. If the aluminum plate is toothick, thermal conductivity may drop.

16) A heat radiator according to any one of pars. 1) to 5), wherein thestress relaxation member is formed of a corrugate aluminum platecomprising wave crest portions, wave trough portions, and connectionportions each connecting the wave crest portion and the wave troughportion, and spaces present between the adjacent connection portionsserve as the stress-absorbing spaces.

17) A heat radiator according to par. 16), wherein a thickness of thecorrugate aluminum plate is 0.05 mm to 1 mm. In the heat radiator ofpar. 17), the thickness of the corrugate aluminum plate is 0.05 mm to 1mm, for the following reason. If the corrugate aluminum plate is toothin, difficulty is involved in processing for obtaining the corrugatealuminum plate, and buckling may arise. If the corrugate aluminum plateis too thick, difficulty is involved in processing for obtaining thecorrugate aluminum plate. In either case, difficulty is involved infinishing for obtaining a predetermined shape.

18) A heat radiator according to par. 16) or 17), wherein at least onecutout portion extending in a direction perpendicular to a longitudinaldirection of the wave crest portions and the wave trough portions isformed at the wave crest portions, the wave trough portions, and theconnection portions of the corrugate aluminum plate.

19) A heat radiator according to par. 16) or 17), wherein a plurality ofthe corrugate aluminum plates are disposed in a longitudinal directionof the wave crest portions and the wave trough portions while beingspaced apart from one another.

20) A heat radiator according to par. 19), wherein the adjacentcorrugate aluminum plates are disposed such that the wave crest portionsand the wave trough portions of one corrugate aluminum plate are shiftedfrom those of the other corrugate aluminum plate in a lateral directionof the wave crest portions and the wave trough portions. 21) A heatradiator according to any one of pars. 6) to 20), wherein the aluminumplate is formed of pure aluminum having a purity of 99% or higher.

22) A heat radiator according to any one of pars. 6) to 21), wherein thestress relaxation member is formed of a brazing sheet which comprises acore, and brazing-material layers covering respective opposite sides ofthe core, and the stress relaxation member is brazed to the insulatingsubstrate or the metal layer of the insulating substrate and to the heatsink by use of the brazing-material layers of the brazing sheet.

23) A heat radiator according to any one of pars. 6) to 21), wherein thestress relaxation member is brazed to the insulating substrate or themetal layer of the insulating substrate and to the heat sink by use of asheetlike brazing material.

24) A power module comprising a heat radiator according to any one ofpars. 1) to 23), and a semiconductor device mounted on the insulatingsubstrate of the heat radiator.

Effects of the Invention

According to the heat radiator of par. 1), the stress relaxation memberformed of a high-thermal-conduction material and having astress-absorbing space intervenes between the insulating substrate andthe heat sink, and the stress relaxation member is metal-bonded to theinsulating substrate and to the heat sink. Thus, excellent thermalconductivity is established between the insulating substrate and theheat sink, thereby improving heat radiation performance for radiatingheat generated by a semiconductor device mounted on the insulatingsubstrate. Furthermore, even when thermal stress arises in the heatradiator from a difference in thermal expansion coefficient between theinsulating substrate and the heat sink, the stress relaxation member isdeformed by the effect of the stress-absorbing space; thus, the thermalstress is relaxed, thereby preventing cracking in the insulatingsubstrate, cracking in a bond zone between the insulating substrate andthe stress relaxation member, or warpage of a bond surface of the heatsink bonded to the insulating substrate. Accordingly, heat radiationperformance is maintained over a long term. Also, use of the stressrelaxation member described in any one of pars. 6) to 20) lowers cost ofthe stress relaxation member, thereby lowering material cost for theheat radiator.

According to the heat radiator of par. 2), the stress relaxation memberis brazed to the insulating substrate and to the heat sink. Thus,bonding of the stress relaxation member and the insulating substrate andbonding of the stress relaxation member and the heat sink can beperformed simultaneously, thereby improving workability in fabricationof the heat radiator. According to the heat radiator described in PatentDocument 1, after the insulating substrate and the heat radiation memberare soldered together, the heat radiation member and the heat sink mustbe screwed together; therefore, workability in fabrication of the heatradiator is poor.

According to the heat radiator of par. 3), the metal layer is formed ona side of the insulating substrate opposite theheat-generating-element-mounting side; the stress relaxation memberformed of a high-thermal-conduction material and having astress-absorbing space intervenes between the metal layer and the heatsink; and the stress relaxation member is metal-bonded to the metallayer of the insulating substrate and to the heat sink. Thus, excellentthermal conductivity is established between the insulating substrate andthe heat sink, thereby improving heat radiation performance forradiating heat generated by a semiconductor device mounted on theinsulating substrate. Furthermore, even when thermal stress arises inthe heat radiator from a difference in thermal expansion coefficientbetween the insulating substrate and the heat sink, the stressrelaxation member is deformed by the effect of the stress-absorbingspace; thus, the thermal stress is relaxed, thereby preventing crackingin the insulating substrate, cracking in a bond zone between the metallayer of the insulating substrate and the stress relaxation member, orwarpage of a bond surface of the heat sink bonded to the insulatingsubstrate. Accordingly, heat radiation performance is maintained over along term. Also, use of the stress relaxation member described in anyone of pars. 6) to 20) lowers cost of the stress relaxation member,thereby lowering material cost for the heat radiator.

According to the heat radiator of par. 4), the stress relaxation memberis brazed to the metal layer of the insulating substrate and to the heatsink. Thus, bonding of the stress relaxation member and the metal layerof the insulating substrate and bonding of the stress relaxation memberand the heat sink can be performed simultaneously, thereby improvingworkability in fabrication of the heat radiator. According to the heatradiator described in Patent Document 1, after the insulating substrateand the heat radiation member are soldered together, the heat radiationmember and the heat sink must be screwed together; therefore,workability in fabrication of the heat radiator is poor.

With the heat radiator of any one of pars. 6) to 20), cost of the stressrelaxation member is lowered, thereby lowering material cost for theheat radiator.

According to the heat radiator of any one of pars. 6) to 9), the stressrelaxation member is deformed by the effect of the stress-absorbingspaces in the form of the through holes; thus, thermal stress isrelaxed.

The heat radiator of par. 7) exhibits excellent thermal-stressrelaxation effect. A largest thermal stress or strain is likely to arisein a perimetric portion of the insulating substrate of the heatradiator. However, by virtue of the configuration of par. 7), a portionof the aluminum plate corresponding to the perimetric portion of theinsulating substrate is apt to be deformed by the effect of the throughholes, thereby relaxing the thermal stress.

According to the heat radiator of par. 10), the stress relaxation memberis deformed by the effect of the stress-absorbing spaces in the form ofthe recesses, thereby relaxing the thermal stress.

The heat radiator of par. 11) exhibits excellent thermal-stressrelaxation effect. A largest thermal stress or strain is likely to arisein a perimetric portion of the insulating substrate of the heatradiator. However, by virtue of the configuration of par. 11), a portionof the aluminum plate corresponding to the perimetric portion of theinsulating substrate is apt to be deformed by the effect of therecesses, thereby relaxing the thermal stress.

According to the heat radiator of par. 14), the stress relaxation memberis deformed by the effect of the stress-absorbing spaces in the form ofrecesses and through holes, thereby relaxing the thermal stress.

According to the heat radiator of par. 16) or 17), the stress relaxationmember is deformed by the effect of the stress-absorbing spaces of thecorrugate aluminum plate, thereby relaxing the thermal stress.

According to the heat radiator of par. 18), the cutout portion enhancesthe thermal-stress relaxation effect.

According to the heat radiator of par. 19), the spaces between theadjacent corrugate aluminum plates enhance the thermal-stress relaxationeffect.

According to the heat radiator of par. 20), the thermal-stressrelaxation effect is enhanced in different directions.

According to the heat radiator of par. 21), wettability of a moltenbrazing material on the stress relaxation member becomes excellent whenthe stress relaxation member and the insulating substrate or the metallayer of the insulating substrate are to be brazed together and when thestress relaxation member and the heat sink are to be brazed together,thereby improving brazing workability. Furthermore, when brazing heatcauses a drop in the strength of the stress relaxation member andgeneration of thermal stress in the heat radiator, the stress relaxationmember is apt to be deformed, thereby yielding excellent stressrelaxation effect.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will next be described withreference to the drawings. The upper and lower sides of FIG. 1 will bereferred to as “upper” and “lower,” respectively. In all the drawings,like features or parts are denoted by like reference numerals, andrepeated description thereof is omitted.

FIG. 1 shows a portion of a power module which uses a heat radiator of afirst embodiment of the present invention. FIG. 2 shows a stressrelaxation member.

In FIG. 1, the power module includes a heat radiator (1) and asemiconductor device (2); for example, an IGBT, mounted on the heatradiator (1).

The heat radiator (1) includes an insulating substrate (3) which isformed of a ceramic and whose upper side serves as aheat-generating-element-mounting side; a stress relaxation member (4)bonded to the lower side of the insulating substrate (3); and a heatsink (5) bonded to the lower side of the stress relaxation member (4).

The insulating substrate (3) may be formed of any ceramic so long as itsatisfies requirements for insulating characteristics, thermalconductivity, and mechanical strength. For example, Al₂O₃ or AlN is usedto form the insulating substrate (3). A circuit layer (6) is formed onthe upper surface of the insulating substrate (3), and the semiconductordevice (2) is soldered onto the circuit layer (6). The solder layer isnot shown. The circuit layer (6) is formed of a metal having excellentelectrical conductivity, such as aluminum or copper. Preferably, thecircuit layer (6) is formed of a pure aluminum having high purity, whichexhibits high electrical conductivity, high deformability, and excellentsolderability in relation to a semiconductor device. A metal layer (7)is formed on the lower surface of the insulating substrate (3). Thestress relaxation member (4) is brazed to the metal layer (7). Thebrazing-material layer is not shown. Preferably, the metal layer (7) isformed of a metal having excellent thermal conductivity, such asaluminum or copper. Preferably, the metal layer (7) is formed of a purealuminum having high purity, which exhibits high thermal conductivity,high deformability, and excellent wettability in relation to a moltenbrazing material. The insulating substrate (3), the circuit layer (6),and the metal layer (7) constitute a power module substrate (8).

The stress relaxation member (4) is formed of a high-thermal-conductionmaterial and has stress-absorbing spaces. As shown in FIG. 2, the stressrelaxation member (4) is formed of an aluminum plate (10) in which aplurality of non-angular holes; herein, circular through holes (9), areformed in a staggered arrangement, and the through holes (9) serve asstress-absorbing spaces. The circular through holes (9) are formed in atleast a portion of the aluminum plate (10) which corresponds to aperimetric portion of the insulating substrate (3); i.e., in the entireregion of the aluminum plate (10), including a perimetric portioncorresponding to the perimetric portion of the insulating substrate (3).Preferably, the aluminum plate (10) is formed of a pure aluminum havinga purity of 99% or higher, desirably 99.5% or higher, which exhibitshigh thermal conductivity, high deformability induced by a drop instrength caused by brazing heat, and excellent wettability in relationto a molten brazing material. The thickness of the aluminum plate (10)is preferably 0.3 mm to 3 mm, more preferably 0.3 mm to 1.5 mm. Thecircle-equivalent diameter of the through holes (9) (here, the diameterof the through holes (9), because the through holes (9) are circular) ispreferably 1 mm to 4 mm. Preferably, the percentage of the total area ofall of the through holes (9) to the area of one side of the aluminumplate (10) is 3% to 50%.

Preferably, the heat sink (5) assumes a flat, hollow shape in which aplurality of cooling-fluid channels (11) are formed in parallel, and isformed of aluminum, which exhibits excellent thermal conductivity and islight. A cooling fluid may be either liquid or gas.

Brazing between the stress relaxation member (4) and the metal layer (7)of the power module substrate (8) and brazing between the stressrelaxation member (4) and the heat sink (5) are performed, for example,as follows. The stress relaxation member (4) is formed of an aluminumbrazing sheet which is composed of a core formed of pure aluminum, andaluminum brazing-material layers covering respective opposite sides ofthe core. Examples of an aluminum brazing-material include an Al—Sialloy and an Al—Si—Mg alloy. Preferably, the thickness of the aluminumbrazing-material layer is about 10 μm to 200 μm. When the thickness istoo small, lack of supply of the brazing material arises, potentiallycausing defective brazing. When the thickness is too large, excesssupply of the brazing material arises, potentially causing generation ofvoids and a drop in thermal conductivity.

Next, the power module substrate (8), the stress relaxation member (4),and the heat sink (5) are arranged in layers and restrained together byuse of an appropriate jig to thereby apply an appropriate load to bondsurfaces. The resultant assembly is heated to 570° C. to 600° C. in avacuum or an inert gas atmosphere. Thus, brazing of the stressrelaxation member (4) and the metal layer (7) of the power modulesubstrate (8) and brazing of the stress relaxation member (4) and theheat sink (5) are performed simultaneously.

Alternatively, brazing of the stress relaxation member (4) and the metallayer (7) of the power module substrate (8) and brazing of the stressrelaxation member (4) and the heat sink (5) may performed as follows.The stress relaxation member (4) is formed of a bare material of theabove-mentioned pure aluminum. The power module substrate (8), thestress relaxation member (4), and the heat sink (5) are arranged inlayers. In this arrangement, a sheetlike aluminum brazing-material of,for example, an Al—Si alloy or an Al—Si—Mg alloy intervenes between thestress relaxation member (4) and the metal layer (7) of the power modulesubstrate (8) and between the stress relaxation member (4) and the heatsink (5). Preferably, the thickness of the sheetlike aluminumbrazing-material is about 10 μm to 200 μm. When the thickness is toosmall, lack of supply of the brazing material arises, potentiallycausing defective brazing. When the thickness is too large, excesssupply of the brazing material arises, potentially causing generation ofvoids and a drop in thermal conductivity. Subsequently, brazing isperformed as in the above-mentioned case of use of the aluminum brazingsheet. Thus, brazing of the stress relaxation member (4) and the metallayer (7) of the power module substrate (8) and brazing of the stressrelaxation member (4) and the heat sink (5) are performedsimultaneously.

FIG. 3 shows a second embodiment of the heat radiator according to thepresent invention.

In the case of a heat radiator (15) shown in FIG. 3, the metal layer (7)is not formed on the lower surface of the insulating substrate (3) ofthe power module substrate (8); i.e., the stress relaxation member (4)is directly brazed to the insulating substrate (3). This brazing isperformed in a manner similar to that of the first embodiment describedabove.

FIGS. 4 to 21 show modified embodiments of the stress relaxation member.

A stress relaxation member (20) shown in FIG. 4 is formed of thealuminum plate (10) in which a plurality of rectangular through holes(21) are formed in a staggered arrangement, and the through holes (21)serve as stress-absorbing spaces. The through holes (21) are formed inat least a portion of the aluminum plate (10) which corresponds to aperimetric portion of the insulating substrate (3); i.e., in the entireregion of the aluminum plate (10), including a perimetric portioncorresponding to the perimetric portion of the insulating substrate (3).Preferably, as in the case of the stress relaxation member (4) shown inFIG. 2, the percentage of the total area of all of the through holes(21) to the area of one side of the aluminum plate (10) is 3% to 50%.

A stress relaxation member (22) shown in FIG. 5 is formed of thealuminum plate (10) in which a plurality of the circular through holes(9) are formed only in a perimetric portion; i.e., in a portioncorresponding to a perimetric portion of the insulating substrate (3).Also, in this case, preferably, as in the case of the stress relaxationmember (4) shown in FIG. 2, the percentage of the total area of all ofthe through holes (9) to the area of one side of the aluminum plate (10)is 3% to 50%.

A stress relaxation member (23) shown in FIG. 6 is formed of thealuminum plate (10) in which a plurality of the circular through holes(9) are formed in two inner and outer rows only in a perimetric portion;i.e., in a portion corresponding to a perimetric portion of theinsulating substrate (3). Also, in this case, preferably, as in the caseof the stress relaxation member (4) shown in FIG. 2, the percentage ofthe total area of all of the through holes (9) to the area of one sideof the aluminum plate (10) is 3% to 50%.

In the stress relaxation members (22) and (23) shown in FIGS. 5 and 6,respectively, the rectangular through holes (21) may be formed in placeof the circular through holes (9). In either case, the through holes (9)and (21) serve as stress-absorbing spaces.

A stress relaxation member (25) shown in FIG. 7 is formed of thealuminum plate (10) in which a plurality of spherical recesses (26) areformed in a staggered arrangement on one side, and the recesses (26)serve as stress-absorbing spaces.

A stress relaxation member (30) shown in FIG. 8 is formed of thealuminum plate (10) in which a plurality of the spherical recesses (26)are formed in vertical and horizontal rows on opposite sides, and therecesses (26) serve as stress-absorbing spaces. The recesses (26) formedon one side of the aluminum plate (10) differ from the recesses (26)formed on the other side in position as viewed in plane.

A stress relaxation member (31) shown in FIG. 9 is formed of thealuminum plate (10) in which a plurality of truncated-cone-shapedrecesses (32) are formed in a staggered arrangement on one side, and therecesses (32) serve as stress-absorbing spaces.

A stress relaxation member (34) shown in FIG. 10 is formed of thealuminum plate (10) in which a plurality of the truncated-cone-shapedrecesses (32) are formed in vertical and horizontal rows on oppositesides, and the recesses (32) serve as stress-absorbing spaces. Therecesses (32) formed on one side of the aluminum plate (10) differ fromthe recesses (32) formed on the other side in position as viewed inplane.

In the stress relaxation members (25), (30), (31), and (34) shown inFIGS. 7 to 10, respectively, the recesses (26) and (32) are formed inthe entire region of the aluminum plate (10), including at least aperimetric portion corresponding to a perimetric portion of theinsulating substrate (3). However, as in the case of the stressrelaxation members (22) and (23) shown in FIGS. 5 and 6, respectively,the recesses (26) and (32) may be formed only in the perimetric portioncorresponding to the perimetric portion of the insulating substrate (3).In the stress relaxation members (25), (30), (31), and (34) shown inFIGS. 7 to 10, respectively, since the openings of the recesses (26) and(32) are circular, the recesses (26) and (32) preferably have acircle-equivalent diameter; i.e., a diameter, of 1 mm to 4 mm.Preferably, the percentage of the total area of openings of all of therecesses (26) or (32) to an area of the side of the aluminum plate (10)on which the recesses (26) or (32) are formed is 3% to 50%.

A stress relaxation member (36) shown in FIG. 11 is formed of thealuminum plate (10) in which a plurality of quadrangular-pyramid-shapedrecesses (37) are formed in a staggered arrangement on one side, and therecesses (37) serve as stress-absorbing spaces.

A stress relaxation member (38) shown in FIG. 12 is formed of thealuminum plate (10) in which a plurality of thequadrangular-pyramid-shaped recesses (37) are formed in vertical andhorizontal rows on opposite sides, and the recesses (37) serve asstress-absorbing spaces. The recesses (37) formed on one side of thealuminum plate (10) differ from the recesses (37) formed on the otherside in position as viewed in plane.

A stress relaxation member (40) shown in FIG. 13 is formed of thealuminum plate (10) in which a plurality ofrectangular-parallelepiped-shaped recesses (41) are formed in verticaland horizontal rows on one side, and the recesses (41) serve asstress-absorbing spaces. Herein, the adjacent recesses (41) in each ofthe vertical rows are arranged such that their longitudinal directionsare oriented 90 degrees different from each other. Similarly, theadjacent recesses (41) in each of the horizontal rows are arranged suchthat their longitudinal directions are oriented 90 degrees differentfrom each other.

A stress relaxation member (42) shown in FIG. 14 is formed of thealuminum plate (10) in which a plurality of therectangular-parallelepiped-shaped recesses (41) are formed in astaggered arrangement on opposite sides, and the recesses (41) serve asstress-absorbing spaces. The recesses (41) formed on one side of thealuminum plate (10) differ from the recesses (41) formed on the otherside in position as viewed in plane. Also, the recesses (41) formed on afirst side of the aluminum plate (10) are arranged such that theirlongitudinal directions are oriented in the same direction, and therecesses (41) formed on a second side of the aluminum plate (10) arearranged such that their longitudinal directions are orientedperpendicularly to those of the recesses (41) formed on the first side.

A stress relaxation member (45) shown in FIG. 15 is formed of thealuminum plate (10) in which a plurality of through holes (46) and (47)are formed, and the through holes (46) and (47) serve asstress-absorbing spaces. In four corner portions of the aluminum plate(10), a plurality of slit-like through holes (46) are formed on aplurality of diagonal lines which are in parallel with one another andintersect with two sides that define each of the corner portions, whilethe slit-like through holes (46) are spaced apart from one another alongthe diagonal lines. In a portion of the aluminum plate (10) other thanthe four corner portions, a plurality of arcuate through holes (47) areformed on a plurality of concentric circles while beingcircumferentially spaced apart from one another. Also, in this stressrelaxation member (45), preferably, the percentage of the total area ofall of the through holes (46) and (47) to the area of one side of thealuminum plate (10) is 3% to 50%.

A stress relaxation member (50) shown in FIG. 16 is formed of thealuminum plate (10) in which a plurality of groove-like recesses (51)are formed on one side, and the recesses (51) serve as stress-absorbingspaces. Some recesses (51) assume the form of connected letter Vs, andother recesses (51) assume the form of a letter V.

A stress relaxation member (53) shown in FIG. 17 is formed of thealuminum plate (10) in which a plurality of V-groove-like recesses (54)and (55) are formed on opposite sides, and the recesses (54) and (55)serve as stress-absorbing spaces. The recesses (54) formed on a firstside of the aluminum plate (10) extend along the longitudinal directionof the aluminum plate (10) and are spaced apart from one another in thelateral direction of the aluminum plate (10). The recesses (55) formedon a second side of the aluminum plate (10) extend along the lateraldirection of the aluminum plate (10) and are spaced apart from oneanother in the longitudinal direction of the aluminum plate (10). Thetotal of the depth of the recesses (54) formed on the first side of thealuminum plate (10) and the depth of the recesses (55) formed on thesecond side of the aluminum plate (10) is less than the thickness of thealuminum plate (10).

A stress relaxation member (57) shown in FIG. 18 is formed of thealuminum plate (10) in which a plurality of V-groove-like recesses (58)and (59) are formed on opposite sides and in which a plurality ofthrough holes (60) are formed, and the recesses (58) and (59) and thethrough holes (60) serve as stress-absorbing spaces. The recesses (58)formed on a first side of the aluminum plate (10) extend along thelongitudinal direction of the aluminum plate (10) and are spaced apartfrom one another in the lateral direction of the aluminum plate (10).The recesses (59) formed on a second side of the aluminum plate (10)extend along the lateral direction of the aluminum plate (10) and arespaced apart from one another in the longitudinal direction of thealuminum plate (10). The total of the depth of the recesses (58) formedon the first side of the aluminum plate (10) and the depth of therecesses (59) formed on the second side of the aluminum plate (10) isgreater than the thickness of the aluminum plate (10), whereby thethrough holes (60) are formed at intersections of the recesses (58) and(59).

The aluminum plate (10) used to form the stress relaxation members shownin FIGS. 4 to 18 is identical with that used to form the stressrelaxation member (4) shown in FIG. 2. Each of the stress relaxationmembers shown in FIGS. 4 to 18 is brazed to the power module substrate(8) and to the heat sink (5) in a manner similar to that of the firstand second embodiments.

A stress relaxation member (63) shown in FIG. 19 is formed of acorrugate aluminum plate (67) which includes wave crest portions (64),wave trough portions (65), and connection portions (66) each connectingthe wave crest portion (64) and the wave trough portion (65), and spacespresent between the adjacent connection portions (66) serve asstress-absorbing spaces. A cutout portion (68) which extends at alaterally central portion of the corrugate aluminum plate (67) in adirection perpendicular to the longitudinal direction of the wave crestportions (64) and the wave trough portions (65) is formed at the wavecrest portions (64), the wave trough portions (65), and the connectionportions (66). Accordingly, the corrugate aluminum plate (67) is dividedinto two portions except for its opposite end portions.

A stress relaxation member (70) shown in FIG. 20 is configured asfollows. A plurality of the cutout portions (68) are formed at the wavecrest portions (64), the wave trough portions (65), and the connectionportions (66) of the corrugate aluminum plate (67) similar to that ofFIG. 19, in such a manner as to extend in a direction perpendicular tothe longitudinal direction of the wave crest portions (64) and the wavetrough portions (65) and to be juxtaposed to one another in the lateraldirection of the corrugate aluminum plate (67). Accordingly, thecorrugate aluminum plate (67) is divided into a plurality of portionsexcept for its opposite end portions.

A stress relaxation member (72) shown in FIG. 21 is configured asfollows. A plurality of; herein, two, corrugate aluminum plates (67) inwhich no cutout is formed are disposed in the longitudinal direction ofthe wave crest portions (64) and the wave trough portions (65) whilebeing spaced apart from one another. No particular limitation is imposedon the number of the corrugate aluminum plates (67). The adjacentcorrugate aluminum plates (67) are disposed such that the wave crestportions (64) and the wave trough portions (65) of one corrugatealuminum plate (67) are shifted from those of the other corrugatealuminum plate (67) in the lateral direction of the wave crest portions(64) and the wave trough portions (65).

In some cases, the stress relaxation member (72) shown in FIG. 21 may beconfigured as follows: the adjacent corrugate aluminum plates (67) aredisposed such that the wave crest portions (64) and the wave troughportions (65) of one corrugate aluminum plate (67) coincide with thoseof the other corrugate aluminum plate (67) with respect to the lateraldirection of the wave crest portions (64) and the wave trough portions(65).

In the stress relaxation members (63), (70), and (72) shown in FIGS. 19to 21, respectively, the thickness of the corrugate aluminum plate (67)is preferably 0.05 mm to 1 mm. As in the case of the stress relaxationmember (4) shown in FIG. 2, preferably, the corrugate aluminum plate(67) is formed of a pure aluminum having a purity of 99% or higher,desirably 99.5% or higher, which exhibits high thermal conductivity andhigh deformability induced by a drop in strength caused by brazing heat.As in the case of the above-described first and second embodiments, eachof the stress relaxation members (63), (70), and (72) shown in FIGS. 19to 21 is brazed to the power module substrate (8) and to the heat sink(5).

INDUSTRIAL APPLICABILITY

The heat radiator of the present invention includes an insulatingsubstrate whose first side serves as a heat-generating-element-mountingside and a heat sink fixed to a second side of the insulating substrate,and is preferably used for radiating, from the heat sink, heat generatedfrom a heat-generating-element, such as a semiconductor device, mountedon the insulating substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Vertical sectional view of a portion of a power module which usesa heat radiator, showing a first embodiment of a heat radiator accordingto the present invention.

FIG. 2 Perspective view showing a stress relaxation member used in theheat radiator of FIG. 1.

FIG. 3 View equivalent to FIG. 1, showing a second embodiment of theheat radiator according to the present invention.

FIG. 4 Perspective view showing a first modified embodiment of thestress relaxation member.

FIG. 5 Partially cutaway perspective view showing a second modifiedembodiment of the stress relaxation member.

FIG. 6 Partially cutaway perspective view showing a third modifiedembodiment of the stress relaxation member.

FIG. 7 Partially cutaway perspective view showing a fourth modifiedembodiment of the stress relaxation member.

FIG. 8 Partially cutaway perspective view showing a fifth modifiedembodiment of the stress relaxation member.

FIG. 9 Partially cutaway perspective view showing a sixth modifiedembodiment of the stress relaxation member.

FIG. 10 Partially cutaway perspective view showing a seventh modifiedembodiment of the stress relaxation member.

FIG. 11 Partially cutaway perspective view showing an eighth modifiedembodiment of the stress relaxation member.

FIG. 12 Partially cutaway perspective view showing a ninth modifiedembodiment of the stress relaxation member.

FIG. 13 Perspective view showing a tenth modified embodiment of thestress relaxation member.

FIG. 14 Perspective view showing an eleventh modified embodiment of thestress relaxation member.

FIG. 15 Perspective view showing a twelfth modified embodiment of thestress relaxation member.

FIG. 16 Perspective view showing a thirteenth modified embodiment of thestress relaxation member.

FIG. 17 Perspective view showing a fourteenth modified embodiment of thestress relaxation member.

FIG. 18 Perspective view showing a fifteenth modified embodiment of thestress relaxation member.

FIG. 19 Perspective view showing a sixteenth modified embodiment of thestress relaxation member.

FIG. 20 Perspective view showing a seventeenth modified embodiment ofthe stress relaxation member.

FIG. 21 Perspective view showing an eighteenth modified embodiment ofthe stress relaxation member.

1. A heat radiator comprising an insulating substrate whose first sideserves as a heat-generating-element-mounting side, and a heat sink fixedto a second side of the insulating substrate; wherein a stressrelaxation member formed of a high-thermal-conduction material andhaving a stress-absorbing space intervenes between the insulatingsubstrate and the heat sink, and the stress relaxation member ismetal-bonded to the insulating substrate and to the heat sink.
 2. A heatradiator according to claim 1, wherein the stress relaxation member isbrazed to the insulating substrate and to the heat sink.
 3. A heatradiator comprising an insulating substrate whose first side serves as aheat-generating-element-mounting side, and a heat sink fixed to a secondside of the insulating substrate; wherein a metal layer is formed on aside of the insulating substrate opposite theheat-generating-element-mounting side; a stress relaxation member formedof a high-thermal-conduction material and having a stress-absorbingspace intervenes between the metal layer and the heat sink; and thestress relaxation member is metal-bonded to the metal layer of theinsulating substrate and to the heat sink.
 4. A heat radiator accordingto claim 3, wherein the stress relaxation member is brazed to the metallayer of the insulating substrate and to the heat sink.
 5. A heatradiator according to claim 1, wherein the insulating substrate isformed of a ceramic.
 6. A heat radiator according to claim 1, whereinthe stress relaxation member is formed of an aluminum plate having aplurality of through holes formed therein, and the through holes serveas the stress-absorbing spaces.
 7. A heat radiator according to claim 6,wherein the through holes are formed in at least a portion of thealuminum plate which corresponds to a perimetric portion of theinsulating substrate.
 8. A heat radiator according to claim 6, whereinthe through holes are of a non-angular shape and have acircle-equivalent diameter of 1 mm to 4 mm.
 9. A heat radiator accordingto claim 6, wherein a percentage of a total area of all of the throughholes to an area of one side of the aluminum plate is 3% to 50%.
 10. Aheat radiator according to claim 3, wherein the stress relaxation memberis formed of an aluminum plate having a plurality of recesses formed onat least either side, and the recesses serve as the stress-absorbingspaces.
 11. A heat radiator according to claim 10, wherein the recessesare formed on at least a portion of the aluminum plate which correspondsto a perimetric portion of the insulating substrate.
 12. A heat radiatoraccording to claim 10, wherein openings of the recesses are of anon-angular shape and have a circle-equivalent diameter of 1 mm to 4 mm.13. A heat radiator according to claim 10, wherein a percentage of atotal area of openings of all of the recesses to an area of a side ofthe aluminum plate on which the recesses are formed is 3% to 50%.
 14. Aheat radiator according to claim 1, wherein the stress relaxation memberis formed of an aluminum plate having a plurality of recesses formed onat least either side and a plurality of through holes formed therein,and the recesses and through holes serve as the stress-absorbing spaces.15. A heat radiator according to claim 6, wherein a thickness of thealuminum plate used to form the stress relaxation member is 0.3 mm to 3mm.
 16. A heat radiator according to claim 1, wherein the stressrelaxation member is formed of a corrugate aluminum plate comprisingwave crest portions, wave trough portions, and connection portions eachconnecting the wave crest portion and the wave trough portion, andspaces present between the adjacent connection portions serve as thestress-absorbing spaces.
 17. A heat radiator according to claim 16,wherein a thickness of the corrugate aluminum plate is 0.05 mm to 1 mm.18. A heat radiator according to claim 16, wherein at least one cutoutportion extending in a direction perpendicular to a longitudinaldirection of the wave crest portions and the wave trough portions isformed at the wave crest portions, the wave trough portions, and theconnection portions of the corrugate aluminum plate.
 19. A heat radiatoraccording to claim 16, wherein a plurality of the corrugate aluminumplates are disposed in a longitudinal direction of the wave crestportions and the wave trough portions while being spaced apart from oneanother.
 20. A heat radiator according to claim 19, wherein the adjacentcorrugate aluminum plates are disposed such that the wave crest portionsand the wave trough portions of one corrugate aluminum plate are shiftedfrom those of the other corrugate aluminum plate in a lateral directionof the wave crest portions and the wave trough portions.
 21. A heatradiator according to claim 6, wherein the aluminum plate is formed ofpure aluminum having a purity of 99% or higher.
 22. A heat radiatoraccording to claim 6, wherein the stress relaxation member is formed ofa brazing sheet which comprises a core, and brazing-material layerscovering respective opposite sides of the core, and the stressrelaxation member is brazed to the insulating substrate or the metallayer of the insulating substrate and to the heat sink by use of thebrazing-material layers of the brazing sheet.
 23. A heat radiatoraccording to claim 6, wherein the stress relaxation member is brazed tothe insulating substrate or the metal layer of the insulating substrateand to the heat sink by use of a sheetlike brazing material.
 24. A powermodule comprising a heat radiator according to claim 1, and asemiconductor device mounted on the insulating substrate of the heatradiator.